When your building the tele exit while the tele entranced is fully built, the upgrade cost is 100 per to upgrade. so 200 metal for level 3 tele.

Found a bug for the Engineer while playing. if you have a tele entrance fully built and then play a tele exit down and upgrade the telepoter entrance a for any amount it will go up a level when the teleporter exit is finsihed building. (for example: Teleporter Entrance [0/200 metal to Upgrade], Teleporter Exit ]Constructing{ Only when first building, not replacing}] Note: For this to work you need to build both teleporters with the eurika effect. You can switch wrenchs and it still be 100 metal to upgrade.